This invention relates to the operation and safety of water cooled nuclear fission reactors, and in particular to measures for reducing the hazards of possible exposure of operating and maintenance personnel to a source of radiation dispersed throughout the coolant water circulating system of such nuclear reactors.
A significant potential hazard in water cooled nuclear fission reactors, such as boiling water reactors, is the spread of radioactive substances throughout the circulating system for the reactor coolant water. Operating personnel and maintenance workers can be subjected to radiation from such extensively dispersed radioactive substances within and about many areas or locations of the nuclear reactor plant. Increased radiation and its dispersion within a reactor plant presents both an elevated health hazard and economic liability due to restricted work time exposure for workers in such area of radiation presence.
Cobalt, derived from a number of different alloys commonly employed in components of the reactor's mechanisms or structures, is subject to induced radioactivity, especially the cobalt-60 isotope. This radioactive cobalt-60 isotope, or ions or compounds thereof, can be carried in the circulating coolant water flowing through the coolant water circuit whereby the radioactive substances are spread and deposited throughout the cooling water circuit or primary loop system of the reactor plant. Such radioactive substances are prone to become taken up and incorporated into the normally occurring oxide films which form and progressively accumulate on the inner coolant water retaining structural surfaces that provide the reactor coolant water circuit.
A number of proposals or potential solutions to this problem of dispersion of radioactive substances throughout the coolant water circuit or system and incorporation into the inherently produced oxide films forming over the surfaces of structures providing the coolant water circuit or system have been considered or made. One approach to controlling the potentially hazardous cobalt source of such radiation has been the application of zinc as disclosed in several U.S. patents, for example U.S. Pat. Nos. 4,756,874, issued Jul. 12, 1988 and 4,759,900, issued Jul. 26, 1988. The disclosure and contents of the aforesaid patents are incorporated herein by reference.